A recently developed Land Grid Array device or package (hereinafter referred to as an LGA device) comprises a rectangular ceramic plate carrying an integrated circuit of high complexity and having arrays of densely packed individual contact pads or lands located adjacent outer edges of a lower face thereof. Such device is susceptible of extreme miniaturization being, for example, 1.2 square inches in area and one tenth of an inch in thickness, while the individual pad or land size may be twenty five thousandths of an inch square (0.025.times.0.025 inches). Three rows of such individual pads may be located within one fifth of an inch of respective edges of the lower face.
Clearly, therefore, great accuracy is required in aligning respective lands with respective contact pads of a circuit board.
In view of the extreme miniaturization required for electronic devices, particularly hand carried devices, severe restrictions are imposed both on across-board and above-board space. There is therefore a requirement for a low profile socket connector for an LGA device that not only occupies very little above-board space but provides the requisite security and accuracy of mounting, at the same time satisfying the requirements of ease of assembly to the circuit board and economic production in high volume by conventional mass production techniques.
U.S. Pat. No. 4,498,721 discloses an electrical connector for a planar electronic device or package comprising a generally rectangular base member providing a device-receiving socket and pressure interface connectors formed as elastomer connectors received in respective apertures in the base member, means for securing the base member on a circuit board, and a spring lid engageable with the securing means for mounting on the base member by engagement with the securing means while pressing the device against the elastomer connector to effect electrical connection between the device, the elastomer connector and the circuit board.
However, disadvantages of the prior connector include the absence of any means positively locating the device in a lateral reference position, in coordinates in its plane. Accurate lateral positioning would, therefore, apparently depend on the closeness or preciseness of the fit of the device in the socket of the base member, which approach imposes severe limitations on the accommodation of even the small variations in dimension which would occur, even in the event of industry standardization, as a result of manufacturing tolerances. In consequence, undesirable limitations are imposed on contact size and density and, absent effective standardization, industry wide compatibility.
Further disadvantages associated with the prior connector follow from the securing means relying on four threaded bolts which are time consuming to apply, with risk of over-tightening, a requirement for considerable above-board space to provide clearance for access during assembly and disassembly; protrusion of the bolt heads above the base member, increasing the intrinsic above-board height; and, the absence of means for reliably retaining the four, separate, elastomer pieces preassembled with the base member, prior to mounting on the circuit board, which increases assembly time.